全文获取类型
收费全文 | 13478篇 |
免费 | 1002篇 |
国内免费 | 7篇 |
出版年
2023年 | 58篇 |
2022年 | 141篇 |
2021年 | 256篇 |
2020年 | 195篇 |
2019年 | 254篇 |
2018年 | 348篇 |
2017年 | 275篇 |
2016年 | 415篇 |
2015年 | 683篇 |
2014年 | 673篇 |
2013年 | 880篇 |
2012年 | 1103篇 |
2011年 | 1029篇 |
2010年 | 684篇 |
2009年 | 606篇 |
2008年 | 735篇 |
2007年 | 716篇 |
2006年 | 664篇 |
2005年 | 622篇 |
2004年 | 583篇 |
2003年 | 484篇 |
2002年 | 462篇 |
2001年 | 203篇 |
2000年 | 153篇 |
1999年 | 182篇 |
1998年 | 161篇 |
1997年 | 133篇 |
1996年 | 93篇 |
1995年 | 106篇 |
1994年 | 95篇 |
1993年 | 89篇 |
1992年 | 101篇 |
1991年 | 113篇 |
1990年 | 109篇 |
1989年 | 92篇 |
1988年 | 73篇 |
1987年 | 72篇 |
1986年 | 72篇 |
1985年 | 60篇 |
1984年 | 81篇 |
1983年 | 58篇 |
1982年 | 54篇 |
1981年 | 47篇 |
1980年 | 32篇 |
1979年 | 41篇 |
1978年 | 36篇 |
1977年 | 34篇 |
1976年 | 34篇 |
1975年 | 44篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Henry C. Stevens Elaine M. Metz Percy Saboya Del Castillo Juan Díaz Alvn Mark T. Bowler 《Journal of Field Ornithology》2019,90(1):70-79
White‐sand forests are patchily distributed ecosystems covering just 5% of Amazonia that host many specialist species of birds not found elsewhere, and these forests are threatened due to their small size and human exploitation of sand for construction projects. As a result, many species of birds that are white‐sand specialists are at risk of extinction, and immediate conservation action is paramount for their survival. Our objective was to evaluate current survey methods and determine the relative effect of the size of patches of these forests on the presence or absence of white‐sand specialists. Using point counts and autonomous recorders, we surveyed avian assemblages occupying patches of white‐sand forest in the Peruvian Amazon in April 2018. Overall, we detected 126 species, including 21 white‐sand forest specialists. We detected significantly more species of birds per survey point with autonomous recorders than point counts. We also found a negative relationship between avian species richness and distance from the edge of patches of white‐sand forest, but a significant, positive relationship when only counting white‐sand specialists. Although we detected more species with autonomous recorders, point counts were more effective for detecting canopy‐dwelling passerines. Therefore, we recommend that investigators conducting surveys for rare and patchily distributed species in the tropics use a mixed‐method approach that incorporates both autonomous recorders and visual observation. Finally, our results suggest that conserving large, continuous patches of white‐sand forest may increase the likelihood of survival of species of birds that are white‐sand specialists. 相似文献
2.
Shira Weingarten-Gabbay Susan Klaeger Siranush Sarkizova Leah R. Pearlman Da-Yuan Chen Kathleen M.E. Gallagher Matthew R. Bauer Hannah B. Taylor W. Augustine Dunn Christina Tarr John Sidney Suzanna Rachimi Hasahn L. Conway Katelin Katsis Yuntong Wang Del Leistritz-Edwards Melissa R. Durkin Christopher H. Tomkins-Tinch Pardis C. Sabeti 《Cell》2021,184(15):3962-3980.e17
- Download : Download high-res image (225KB)
- Download : Download full-size image
3.
Capillary permeability in the pancreas and colon: restriction of exogenous and endogenous molecules by fenestrated endothelia 总被引:1,自引:0,他引:1
The permeability properties of fenestrated capillaries in the colon and exocrine and endocrine pancreas to exogenous and endogenous molecules were examined. The exogenous tracers horseradish peroxidase (Einstein-Stokes radius [ESR], 3.0 nm), hemoglobin (ESR, 3.2 nm), and ferritin (ESR, 6.1 nm) were injected intravenously and allowed to circulate for 5-90 min. Tissues were removed and processed for cytochemical or standard electron microscopic examination. The endogenous plasma proteins albumin (ESR, 3.5 nm) and IgG (ESR, 5.5 nm) were localized by immunocytochemistry using the protein A-gold technique. All vessels examined were permeable to HRP in less than 5 min. In contrast, these vessels were restrictive to the slightly larger hemoglobin molecule (60-min circulation) and to ferritin (90-min circulation). Capillaries in the exocrine and endocrine pancreas were restrictive to albumin and IgG. These results demonstrate the presence of fenestrated capillary beds, in addition to the choriocapillaris, that are restrictive to molecules with ESR greater than or equal to 3.2 nm. Capillaries in the mucosa of the colon were restrictive to hemoglobin and ferritin but did not restrict albumin or IgG. This indicates that these vessels are of the permeable type. However, the rate of transendothelial movement of molecules is slower than that of other permeable vessels, such as in the ileo-jejunum. This study has provided further evidence for the existence of fenestrated endothelia that are restrictive to exogenous and/or endogenous molecules. 相似文献
4.
5.
Francisco Gutirrez‐Corchero M. Victoria Arruga Lourdes Sanz Cristina García M. Angeles Hernndez Francisco Campos 《Molecular ecology resources》2002,2(1):75-77
FTA® cards were used for long‐term storage of avian blood samples. Blood DNA was extracted by a simple method and used in PCR for sex identification of adult and nestling Great Grey Shrikes Lanius excubitor. 相似文献
6.
7.
8.
Antonella Canini Lorena Canuti Maria Grilli Caiola Maddalena Del Gallo 《Annals of microbiology》2006,56(4):393-398
In the present work an immunocytochemical characterisation of four endophytic bacterial species has been made by using polyclonal antiserum produced against each of the four bacterial strains previously heated at 60 °C. The aim of this researchsito identify common elements among bacteria associated with their endophytic behaviour. Analysis of extracts of each strain by immunoblotting and ELISA confirmed the presence of proteins from different bacterial strains made up of common epitopes. However, antisaproduced againstHerbaspirillum seropedicae andBurkholderia ambifaria show a high number of bands recognised on each extracts, while antisera againstAzospirillum brasilense andGluconacetobacter diazotrophicus show a low number of bands recognised on each extract. Immunogold labelling showed that epitopes are located both on the cell wall and in the cytoplasm; most likely they could be preursor cell wall proteins synthesized inside the cytoplasm and subsequently transported onto cell wall. Finally, the common bands amog bacterial strains revealed by immunoblotting could play a role as active hydrolases involved in host tissue penetration. 相似文献
9.